Such communication network is known per se.
In use, one or more sources are directly or indirectly connected with the switch. If a source is directly connected with a switch, direct connections, referred to as paths, are for example present between the source and the switch. If a source is indirectly connected with the switch at least one other switch is present between the switch and the source. Between two switches there are often two mutually different routing paths. Each data packet generally comprises information with respect to the source the data packet originates from as well as information related to the destination address where to the data packet is sent. Each switch of the network is capable of extracting the information related to the destination address enabling the switch to forward the data packet into the right direction. Each switch is generally also capable of extracting from the data packet the source from which the packet originates.
In practice, there usually is a difference in length of time used for transferring a data packet originating from the source to the switch depending on the path used. The path followed over the network may sometimes have to be altered quickly during the transit of a number of data packets originating from the source. This need for a quick alteration of the path may, for instance, be a result of a link failure, a result of a desire to use a faster path, or the result of management action leading to the use of a different path. Such a quick change of a path may at some point in time lead to an arrival of the data packets at the switch in an order which is different from the order in which they were sent by the source.
For instance, let's assume that data packet X with a destination address B is sent from the source A before data packet Y with a destination address B is sent from the source A and that a change of path occurs during the transit of packet X and packet Y. If this change only leads to a new path for Y and this new path for Y is faster than the path used by X, packet Y will at some point arrive at the switch before packet X has arrived at that switch. In some uses of the network, such as the use of the network as a bridged Ethernet network, this re-ordering of the data packets during the transit causes problems with regard to the interpretation of such a re-ordered series of data packets at the final destination address B.
It should be noted that within the context of this specification data packets are said to have been re-ordered and an order of data packets is said to be different from an other order of the very same data packets if at least one data packet which was sent before an other data packet is received by a switch or a destination address after the other data packet has been received by that switch.
The problem of re-ordering during transit may be solved by providing each data packet with a sequence number to allow for ordering the data packets back into the order according to which the data packets were sent by the switch. This occurs in protocols such as TCP/IP. However, this leads to extra overhead in the length of a data packet and the packet processing.
It is an object of the invention to provide a communication network with a switch which is arranged to prevent re-ordering of data packets.